Solid-state image pick-up device and imaging system using the same

ABSTRACT

The present invention provides a solid-state image pick-up device without shading in the dark state, and capable of making a dynamic range and a S/N high. Reference numeral  505  denotes an N-type cathode of a photodiode,  506  denoting a surface P-type region for forming the photodiode into an embedded structure,  508   a  denoting an N-type high concentration region which forms a floating diffusion and which is also a drain region of a transfer MOS transistor. Reference character  508   b  denotes a polysilicon lead-out electrode brought into direct contact with the N-type high concentration region. Light incident from the surface passes through an aperture without a metal third layer  525  to enter into the photodiode. Among incident lights, light reflected by the top surface of a gate electrode  504  of the transfer MOS transistor is reflected by a first layer metal  521  right above the polysilicon, so as to repeats reflection a plurality of times to attenuate sufficiently before entering into the floating diffusion section, thereby making the aliasing extremely small.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pick-up device usedfor a digital camera, etc., as an image pick-up device for inputting apicture.

2. Related Background Art

In recent years, there has been a rapidly increasing demand on asolid-state image pick-up device used mainly for a digital still cameraand a video camcorder, as an image pick-up device for inputting apicture.

As such solid-state image pick-up device, CCD (Charge Coupled Device)and MOS type sensors are used. Although the former, which has a highsensitivity and a low noise level in comparison with the latter, hasbeen widely used as an image pick-up device of high picture quality, theformer has disadvantages such as a large power consumption, a high drivevoltage, a high cost due to the fact that the ordinary semiconductormanufacturing process cannot be applied, and a difficulty in integratingperipheral circuits such as a drive circuit, as a result of which theMOS type solid-state image pick-up device, which is capable ofpreventing the above described disadvantages, is expected to be employedin the application for portable devices for which new demands areexpected.

The CMOS solid-state image pick-up device, which is formed by the CMOSprocess, has been put in practical use as a representative of the MOStype solid-state image pick-up devices. A pixel circuit of the CMOSsolid-state image pick-up device is shown in FIG. 1, a plane layout ofthe pixel is shown in FIG. 2, and a cross-sectional structure of thepixel is shown in FIG. 3.

In FIG. 1, reference numeral 1 denotes a photodiode, 2 denoting atransfer MOS transistor for transferring a charge of the photodiode, 3denoting a floating diffusion for temporarily storing the transferredcharge, 4 denoting a reset MOS transistor for resetting the floatingdiffusion and the photodiode, 5 denoting a selection MOS transistor forselecting an arbitrary one line in an array, 6 denoting a sourcefollower MOS transistor for converting the charge of the floatingdiffusion into a voltage and for amplifying the voltage by a sourcefollower amplifier, 7 denoting a read line, which is common to a column,for reading out pixel voltage signals, and 8 denoting a constant currentsource for making a constant current flow in the read line.

A brief description of the operation of the circuit will be providedbelow. Incident light is converted into an electric charge by thephotodiode 1, and the charge is stored in the floating diffusion 3 bythe transfer MOS transistor 2. Since the floating diffusion 3 and thephotodiode 1 are reset to a constant potential by turning off the resetMOS transistor 4 and the transfer MOS transistor 2 beforehand, thepotential of the floating diffusion 3 is changed in accordance with thecharge generated by the incident light. The potential of the floatingdiffusion 3 is amplified by the source follower MOS transistor 6 and isoutputted to the read line 7. The pixel is chosen by turning off theselection MOS transistor 5. An output circuit (not shown) performs adifferential operation between the reset potential of the floatingdiffusion 3 and the potential after the light signal is stored, so as todetect the light signal component.

FIG. 2 shows an example of a layout of the pixel circuit shown inFIG. 1. Reference numeral 10 denotes an active area in which aphotodiode is formed, and 11 denotes an active area in which a selectionMOS transistor and a source follower transistor are formed. Referencenumeral 20 denotes an area of a transfer MOS transistor, and 21 denotesa gate line of the transfer MOS transistor. An area 30 surrounded by abroken line indicates a portion formed of a PN junction of semiconductorin a floating diffusion. Reference numeral 31 also denotes a contact forleading out an electrode from the floating diffusion, 32 denoting ametallic electrode for leading out the floating diffusion, 33 denoting acontact for connecting the metallic electrode 32 to a polysilicon, and34 denoting a polysilicon electrode. Reference numeral 40 denotes areset MOS transistor area and 41 denoting a contact for connection witha reset power supply. Reference numeral 50 denotes a gate area of theselection MOS transistor, 51 denoting a contact for connecting with aVDD power supply, 60 denoting an area of a source follower MOStransistor, of which gate electrode is formed by the polysilicon 34electrically connected with the floating diffusion. Reference numeral 70denotes an output line configured by a metal electrode. Referencenumeral 71 denotes a contact for connecting the output line 70 with themain electrode of the source follower MOS transistor 60.

FIG. 3 is a cross sectional view taken along the line 3-3 in the layoutshown in FIG. 2. Reference numeral 301 denotes an n-type siliconsubstrate, 302 a denoting a P-type well and 302 b denoting a P-typeembedded layer, 303 a denoting a gate oxide film of the MOS transistor,303 b denoting a thin oxide film on the light receiving section, 304denoting a gate electrode of the transfer MOS transistor, 305 denotingan N-type cathode of the photodiode 1, 306 denoting a surface P-typeregion for forming the photodiode into an embedded structure, 307 adenoting an LOCOS oxide film for element isolation, 307 b denoting aP-type channel stop layer, 308 denoting a N-type high concentrationregion which forms the floating diffusion 3 and which is also the drainregion of the transfer MOS transistor 2, 309 denoting a silicon oxidefilm for insulating the gate electrode from a metal first layer, 320denoting a contact plug, 321 denoting the metal first layer, 322denoting an interlayer insulating film for insulating the metal firstlayer from a metal second layer, 323 denoting the metal second layer,324 denoting an interlayer insulating film for insulating the metalsecond layer from a metal third layer, 325 denoting the metal thirdlayer and 326 denoting a passivation film. In addition, in a colorphotoelectric converter, a color filter layer (not shown) and further amicro lens for improving the sensitivity are formed on the upper layerof the passivation film 326.

Light incident from the surface passes through an aperture without themetal third layer to enter into the photodiode. The light is absorbed inthe N-type anode 305 of the photodiode or in the P-type well 302 a togenerate electron-hole pairs. Among the electron-hole pairs, electronsare stored in the N-type anode region.

However, the above described conventional CMOS solid-state image pick-updevice has a disadvantage that signal electrons generated by theincident light is mixed into the floating diffusion 3 to cause theoutput voltage to fluctuate. As shown in FIG. 3, among electron-holepairs 330 b generated below the gate of the transfer MOS transistor byan obliquely incident light beam 330 a, the electrons are attracted fromthe N-type cathode 305 of the photodiode to the N type highconcentration layer 308 constituting the floating diffusion. Moreover,light 331 a incident on the gate electrode 304 of the transfer MOStransistor, for example, is repeatedly reflected as shown in FIG. 3 togenerate electron-hole pairs 331 b immediately below the N type highconcentration layer 308. Among the electron-hole pairs, the electronsare attracted to the N type high concentration layer. When the firstlayer metal 320 in FIG. 3 is extended to the aperture side to improvethe shading characteristic, the electrostatic capacity of the floatingdiffusion section is increased so as to reduce the charge conversioncoefficient, resulting in a problem of degrading an S/N.

As described above, the electrons directly captured in the floatingdiffusion without passing through the photodiode generate aliasing tocause problems in a solid-state image pick-up device, such as increasingnoise, reducing a dynamic range, increasing output and shading in thedark state. For this reason, improving the shading characteristic of thefloating diffusion has been a problem to be solved in the conventionalCMOS solid-state image pick-up device.

In the CCD type solid-state image pick-up device, a source followeramplifier, in which the floating diffusion is used at the last stage ofthe readout circuit, is also generally used. For example, an example isdisclosed in Japanese Patent Application Laid-Open No. H03-116840, inwhich leading-out of electrodes for the source follower amplifier iseffected with a polysilicon. In this example, however, improvement inthe shading characteristic is not described, and also the fact thatelectrons generated in the silicon flow into the floating diffusion, asdescribed in the above example of the prior art, is not taken intoaccount. Moreover, in the CCD-type solid-state image pick-up device,since only one floating diffusion amplifier is provided on thepost-stage of a horizontal CCD and is located apart from the pixelsection, the layout can be performed without being limited by the pixelarea, and hence a special device is not needed.

On the other hand, in the CMOS solid-state image pick-up device, thereare conditions that the photodiode is arranged close to the floatingdiffusion because the floating diffusion is present in each pixel, andthat a slight gap must be inevitably provided for the metallicelectrodes serving as the light shield because the metallic electrodesare also used as wiring of the circuit, etc., the conditions beingdifferent from those in the CCD-type solid-state image pick-up device,as a result of which a new structural design is needed.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asolid-state image pick-up device without shading in the dark state andcapable of enhancing a dynamic range and an S/N, by improving theshading characteristic of the floating diffusion.

In order to solve the above described problem, a first aspect of thepresent invention is, in a solid-state image pick-up device in which aplurality of pixels, each provided with a photoelectric conversionsection and a signal amplifying section are arranged in an array form,and in which a floating diffusion arranged for each of the pixels oreach of a plurality of the pixels serves as an input of the signalamplifying section,

characterized in that at least a part of connection from the floatingdiffusion to the signal amplifying section is effected by using directcontact of the floating diffusion with a polysilicon, and in that thefloating diffusion is shaded by a metal layer which is not electricallyconnected with the floating diffusion.

Further, a second aspect of the present invention is, in a solid-stateimage pick-up device in which a plurality of pixels, each provided witha photoelectric conversion section and a signal amplifying section, arearranged in an array form, and in which a floating diffusion arrangedfor each of the pixels or each of a plurality of the pixels serves as aninput of the signal amplifying section, characterized in that at least apart of connection from the floating diffusion to the signal amplifyingsection is effected by using direct contact of the floating diffusionwith a polysilicon, and in that a potential barrier is provided betweenthe photoelectric conversion section and the floating diffusion.

Further, a third aspect of the present invention is, in the solid-stateimage pick-up device according to the first and second aspects,characterized in that the connection from the floating diffusion to theinput of the signal amplifying section is effected only with thepolysilicon.

Further, a fourth aspect of the present invention is characterized inthat a metal layer for shading the floating diffusion is a metal layerclosest to the floating diffusion.

Further, a fifth aspect of the present invention is, in the solid-stateimage pick-up device according to the fourth aspect, characterized inthat the metal layer closest to the floating diffusion is provided witha reflectivity lower than that of other layers of the metal layer.

Further, a sixth aspect of the present invention is, in the solid-stateimage pick-up device according to the fourth aspect, characterized inthat the polysilicon is configured by a plurality of layers, of whichuppermost layer has a transmissivity in the region of visible lightlower than that of the other layers of polysilicon.

Further, a seventh aspect of the present invention is, in thesolid-state image pick-up device according to the present invention,characterized in that a potential barrier, for preventing the signalcharges generated in the photoelectric conversion section from flowinginto the floating diffusion, is provided between the photoelectricconversion section and the floating diffusion.

Further, a eighth aspect of the present invention is, in the solid-stateimage pick-up device according to the present invention, characterizedin that resetting means and charge transfer means are provided for eachpixel, and in that the transfer of the signal charges stored in thephotoelectric conversion section to the floating diffusion issimultaneously performed in all pixels after all pixels are reset at thesame time, for making the potential of the floating diffusionsuccessively read out.

Further, according to a ninth aspect of the present invention, there isprovided an image pick-up system comprising: the solid-state imagepick-up device according to the present invention; an image formingoptical system for forming light from a subject into an image; and asignal processing circuit for performing digital conversion andprocessing of output signals from the solid-state image pick-up device.

According to an effect of the first aspect of the present invention, inthe solid-state image pick-up device in which a plurality of pixels,each provided with a photoelectric conversion section and a signalamplifying section, are arranged in an array form, and in which afloating diffusion arranged for each of the pixels or each of aplurality of the pixels serves as an input of the signal amplifyingsection,

since at least a part of connection from the floating diffusion to thesignal amplifying section is effected by using direct contact of thefloating diffusion with a polysilicon and

the floating diffusion is shaded by a metal layer which is notelectrically connected with the floating diffusion, the quantity oflight directly incident on the floating diffusion can be reduced and theparasitic capacitance of the floating diffusion section which isgenerated between the metal layer and the other conductive layers is notincreased, thereby enabling a high S/N to be maintained.

According to an effect of the second aspect of the present invention, ina solid-state image pick-up device in which a plurality of pixels, eachprovided with a photoelectric conversion section and a signal amplifyingsection, are arranged in an array form, and in which a floatingdiffusion arranged for each of the pixels or each of a plurality of thepixels serves as an input of the signal amplifying section,

since at least a part of connection from the floating diffusion to thesignal amplifying section is effected by using direct contact of thefloating diffusion with a polysilicon and a potential barrier isprovided between the photoelectric conversion section and the floatingdiffusion, the quantity of light directly incident on the floatingdiffusion can be reduced by shading the floating diffusion with thefirst layer metal, and the diffusion of signal charges generated in thesilicon into the floating diffusion can be suppressed.

According to an effect of the third aspect of the present invention,since the connection from the floating diffusion to the input of thesignal amplifying section is effected only with the polysilicon, shadingcan be effected without providing a gap in the first layer metal andalso a space for connecting from the polysilicon to the first layermetal can be eliminated so as to enable the floating diffusion to bemade small.

According to an effect of the fourth aspect of the present invention,since the metal layer for shading the floating diffusion is a metallayer closest to the floating diffusion, the amount of light incidentfrom above the floating diffusion can be minimized.

According to an effect of the fifth aspect of the present invention,since the lower most metal layer is configured by a plurality of layersand is provided with a reflectivity lower than that of other layers ofthe metal layer, the quantity of light incident on the floatingdiffusion due to the light reflected on the base surface of the metallayer can be reduced.

According to an effect of the sixth aspect of the present invention, inthe fourth aspect of the invention, the polysilicon is configured by aplurality of layers, of which uppermost layer has a transmissivity inthe visible light area lower than that of the other layers ofpolysilicon, so that the quantity of light which is incident on thefloating diffusion by repeating reflections after reflected on thesurface of the polysilicon, can be reduced.

According to an effect of the seventh aspect of the present invention,in the first aspect of the present invention, since a potential barrierfor preventing the signal charges generated in the photoelectricconversion section from flowing into the floating diffusion, is providedbetween the photoelectric conversion section and the floating diffusion,the diffusion of the signal charges generated in the silicon into thefloating diffusion can be suppressed.

According to an effect of the eighth aspect of the present invention, inthe first and second aspects of the invention, since resetting means andcharge transfer means are provided for each pixel, and the transfer ofsignal charges stored in the photoelectric conversion section to thefloating diffusion is simultaneously performed in all pixels after allpixels are reset at the same time, and then the potential of thefloating diffusion is made to be successively read out so as to enablean electronic shutter of whole picture simultaneous storage type tooperate, an operation of the electronic shutter for enabling asolid-state image pick-up device to perform imaging of high picturequality can be realized without a complicated pixel circuit.

According to the present invention, the shading characteristic of thefloating diffusion of the solid-state image pick-up device can beimproved. As a result, the dynamic range and S/N can be raised withoutcausing shading in the dark state. Further, with the use of the presentinvention, in the solid-state image pick-up device, the electronicshutter of all pixels simultaneous storage type with high picturequality can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a pixel circuit of a conventional CMOS solid-state imagepick-up device;

FIG. 2 is an example of a pixel layout of the conventional CMOSsolid-state image pick-up device;

FIG. 3 is a sectional view of a pixel of the conventional CMOSsolid-state image pick-up device;

FIG. 4 is an example of a pixel layout of a CMOS solid-state imagepick-up device of a first embodiment according to the present invention;

FIG. 5 is a sectional view of the CMOS solid-state image pick-up deviceof the first embodiment according to the present invention;

FIG. 6 is a sectional view of a CMOS solid-state image pick-up device ofa second embodiment according to the present invention;

FIG. 7 is a sectional view of a CMOS solid-state image pick-up device ofa third embodiment according to the present invention;

FIG. 8 is a circuit constitution figure of a CMOS solid-state imagepick-up device according to the present invention;

FIG. 9 is a timing chart of the operation of an electronic shutter ofall pixels simultaneous storage type using the CMOS solid-state imagepick-up device according to the present invention; and

FIG. 10 is a block diagram showing a configuration of a camera systemusing the CMOS solid-state image pick-up device according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the best mode for carrying out the present invention is explainedwith reference to the drawings.

First Embodiment

FIG. 4 shows a layout of a pixel circuit for explaining a firstembodiment according to the present invention. Reference numeral 110denotes an active area in which a photodiode is formed, and 111 denotesan active area in which a selection MOS transistor and a source followertransistor are formed. Reference numeral 120 denotes an area of atransfer MOS transistor and 121 denotes a gate line of the transfer MOStransistor. An area 130 surrounded by a broken line shows a portionformed of a PN junction of semiconductor in the floating diffusion.

A difference from the prior art form is that leading-out of an electrodefrom the floating diffusion is effected by a direct contact with apolysilicon 131. The polysilicon 131 serves directly as a gate electrodeof a source follower MOS transistor with no intermediary of a metallicelectrode. Reference numeral 132 denotes a shading metal covering overthe floating diffusion, which shading metal in the present embodimentcovers in oversize over the gate electrode of the transfer transistorsection 120 and the P-N junction section 130 of the floating diffusion.In this way, it is possible to shade the floating diffusion in aposition close to the silicon by leading out the floating diffusion withthe polysilicon. The floating diffusion may be made to be in anelectrically floating state, or to have a fixed potential by connectingit with a second layer metal or a third layer metal. The other parts arethe same as those in FIG. 2, and reference numeral 140 denotes a resetMOS transistor area, 141 denoting a contact for connecting with a resetpower supply, 150 denoting a gate area of the selection MOS transistor,151 denoting a contact for connecting with a VDD power supply, 160denoting the source follower MOS transistor area, of which gateelectrode is formed by the polysilicon 131 electrically connected withthe floating diffusion. Reference numeral 170 denotes an output lineformed by a metallic electrode. Reference numeral 171 also denotes acontact for connecting the output line 170 with the main electrode ofthe source follower MOS transistor 160.

FIG. 5 is a cross sectional view taken along the line 5-5 in FIG. 4.Reference numeral 501 denotes an n-type silicon substrate, 502 adenoting a P-type well, 502 b denoting a P-type embedded layer, 503 adenoting a gate oxide film of a MOS transistor, 503 b denoting a thinoxide film on a light receiving section, 504 denoting a gate electrodeof a transfer MOS transistor, 505 denoting an N-type cathode of thephotodiode 1, 506 denoting a surface P-type region for forming thephotodiode into an embedded structure, 507 a denoting a LOCOS oxide filmfor element isolation, 507 b denoting a P-type channel stop layer, 508 adenoting an N-type high concentration region which forms the floatingdiffusion and which is also a drain region of the transfer MOStransistor. Reference character 508 b denotes a polysilicon lead-outelectrode brought into direct contact with the N-type high concentrationregion. Reference numeral 509 denotes a silicon oxide film forinsulating the gate electrode from a metal first layer, and 521 denotesthe metal first layer for shading the floating diffusion section.Reference numeral 522 denotes an interlayer insulating film forinsulating the metal first layer from a metal second layer, 523 denotingthe metal second layer, 524 denoting an interlayer insulating film forinsulating the metal second layer from a metal third layer, 525 denotingthe metal third layer, and 526 denoting a passivation film. In a colorphotoelectric converter, a color filter layer (not shown) and also amicro lens for improving the sensibility are further formed on the upperlayer of the passivation film 526, as in the prior art.

Light incident from the surface passes through an aperture without themetal third layer to enter into the photodiode. Among the incidentlights, a light reflected by the top surface of the gate electrode 504of the transfer MOS transistor is reflected by the first layer metalright above the polysilicon, as shown in FIG. 5, so as to repeat aplurality of reflections to attenuate sufficiently before entering intothe floating diffusion section, thereby making the aliasing extremelysmall. In addition, the floating diffusion, which is covered with ametal without a gap as shown in FIG. 4, has a high light shieldingperformance for light traveling a path other than that shown in thecross sectional view in FIG. 5.

The first layer metal is usually formed of aluminum or of an alloymainly made of aluminum, but in order to make the effects of the presentinvention remarkable, the lowermost layer of the first layer metal ispreferably formed of TiN so as to lower the reflectance to the straylight. TiN also serves as a barrier metal, and hence is a materialsuitable for forming minute electric wirings.

According to the present embodiment, the shading characteristic of thefloating diffusion can be improved, and the effect of the aliasing canbe eliminated.

FIG. 8 is the schematic representation of a circuit configuration inwhich a number of pixel circuits according to the present invention aretwo-dimensionally arranged. A pixel 801 includes a photodiode 802, atransfer MOS transistor 803, a source follower MOS transistor 804, areset MOS transistor 805, and a selection MOS transistor 806. Gates ofthe selection MOS transistors in the same row are connected to aselection line 807, gates of the reset MOS transistors in the same roware connected to a reset line 808 and gates of the transfer MOStransistors in the same row are connected to a transfer line 809,respectively, each of the gates in the same row being scanned andselected by a vertical scanning circuit 801. A current source 812 isconnected to an output line 811 in the same column, and the potential ofthe output line can be read out by the source follower operation. Lightsignals are stored in a charge storage section 818 by a light signaltransfer MOS transistor 813 selected by a light signal read line 815,and noise signals are stored in the charge storage section 818 by anoise signal transfer MOS transistor 814 selected by a noise signal readline 816, respectively. The signals stored in the charge storage section818 are sequentially scanned and read out by the horizontal scanningcircuit, and the difference between the light signal and the noisesignal is outputted by a differential amplifier circuit (not shown).

According to the present invention, a significant effect can be obtainedin the case where an electronic shutter of all pixel simultaneousstorage type is operated with a CMOS solid-state image pick-up device.FIG. 9 shows a timing chart of the operation of the electronic shutter.First, in order to reset the photodiode of all pixels, the reset pulsefor all rows is put ON and the transfer pulse for all rows is put ON.From the moment that both pulses are put OFF, photodiodes over theentire screen start the storing operation at the same time. After thestoring operation is performed for a desired period and then thetransfer pulse for all rows is put ON, the signal charge of each pixelis transferred to the floating diffusion of each pixel simultaneously byputting the transfer pulse for all rows OFF. Next, by putting theselection pulse ON/OFF for each row, the charge of the floatingdiffusion is sequentially read out for each row. The read-out signalsare stored as “S+N” signals in the charge storage section 818 in FIG. 8.

Next, by putting the reset pulse for all rows ON, the floating diffusionof all pixels is reset at the same time. After putting the reset pulseOFF, the potential of the floating diffusion of each row is sequentiallyread out. The read-out signals are stored as “N” signals in acapacitance section provided adjacent to the “S+N” in the charge storagesection 818. “S” signal is taken out by inputting the stored “S+N” and“N” signals to the differential amplifier.

Since in this operation a time period during which the charge is storedin the floating diffusion is different for each row, in the conventionalstructure, a row having a long storage period (in this case, the lastline) has an output potential shaded by the aliasing entering into thefloating diffusion, as compared with a row with a short storage period(in this case, the first line). Since the present invention makes itpossible to suppress the aliasing entering into the floating diffusion,such shading is not caused or made to be a level causing no problem.

FIG. 10 shows an example of a circuit block in the case where asolid-state image pick-up device according to the present invention isapplied to a camera. A shutter 1001 is provided in the front side of alens 1002 so as to control exposure. Light quantity is controlled by adiaphragm 1003 as required, and an image is formed on a solid-stateimage pick-up device 1004. A signal outputted from the solid-state imagepick-up device 1004 is processed by a circuit processing image pick-upsignal 1005, and is converted from an analog signal into a digitalsignal by an A/D converter 1006. The output signal is further subjectedto arithmetic processing by a signal processor 1007. The processeddigital signal is stored in a memory unit 1010, and is sent to anexternal device through an external I/F unit 1013. The solid-state imagepick-up device 1004, the circuit processing image pick-up signal 1005,the A/D converter 1006, and the signal processor 1007 are controlled bya timing generator 1008, and also the whole system is controlled by aunit controlling whole structure and arithmetic operation 1009. In orderto record a picture in a recording medium 1012, an output digital signalis recorded through an I/F unit controlling recording medium 1011controlled by the unit controlling whole structure and arithmeticoperation.

In addition, it goes without saying that the present invention can beapplied to the case where a hole storage type pixel is configured byinverting all other conductivity types in the present embodiment.

Second Embodiment

FIG. 6 is a sectional view of a pixel section of a solid-state imagepick-up device of a second embodiment according to the presentinvention. Reference numeral 601 denotes an n-type silicon substrate,602 a denoting a P-type well, 602 b denoting a P-type embedded layer,603 a denoting a gate oxide film of a MOS transistor, 603 b denoting athin oxide film on a light receiving section, 604 denoting a gateelectrode of a transfer MOS transistor, 605 denoting an N-type cathodeof the photodiode 1, 606 denoting a surface P-type region for making thephotodiode formed into an embedded structure, 607 a denoting a LOCOSoxide film for element isolation, 607 b denoting a P-type channel stoplayer, and 608 a denoting an N-type high concentration region whichforms a floating diffusion and which is also formed to be a drain regionof the transfer MOS transistor. Reference character 608 b denotes apolysilicon lead-out electrode brought into direct contact with theN-type high concentration region. The top surface of the polysiliconlead-out electrode 608 b is formed of a metal. Reference character 608 cdenotes, for example, a silicide formed of Ti, W, or Mo. Also, referencenumeral 609 denotes silicon oxide film insulating the gate electrodefrom a metal first layer, 621 denoting the metal first layer shading thefloating diffusion section. Reference numeral 622 denotes an interlayerinsulating film insulating the metal first layer from a metal secondlayer, 623 denoting the metal second layer, 624 denoting an interlayerinsulating film insulating the metal second layer from a metal thirdlayer, 625 denoting the metal third layer and 626 denoting a passivationfilm.

According to the present embodiment, light entering into the floatingdiffusion is further reduced by making the top surface of thepolysilicon electrode low in reflection to the visible light. That is,among incident lights, the light incident on the gate electrode 604 ofthe transfer MOS transistor is not transmitted, so that light directlyentering into the silicon is reduced. In addition, the intensity of thereflected light can also be reduced by suppressing the reflectance ofthe silicide 608 c low. Since the top surface of the polysilicon directcontact 608 b is also covered by silicide, even when there is a straylight, components of the light directly passing through the polysiliconcan be made small.

Third Embodiment

FIG. 7 is a sectional view of a pixel section of a solid-state imagepick-up device of a third embodiment according to the present invention.Reference numeral 701 denotes an N type silicon substrate, 702 denotinga embedded P-type high concentration layer, 703 a denoting an N-typeepitaxial layer, 703 b denoting an N-type cathode of a photodiode, 704a, 704 b, 704 c denoting P-type isolation layers, and 705 a, 705 b, 705c denoting P-type well layers. Reference characters 706 a, 706 b denotechannel stop P-type layers below a field oxide film. Reference numeral714 denotes a field stop layer defining a charge transfer path to afloating diffusion to form a potential barrier directly under a transferMOS transistor, 707 denoting the field oxide film, 708 denoting a gateoxide film of a MOS transistor, 709 a denoting a gate polysilicon of thetransfer MOS transistor, on which surface a metal silicide layer 709 bis provided and 710 denoting a surface P-type layer for forming thephotodiode into a embedded type. Reference numeral 711 denotes an N-typehigh concentration diffusion region of the transfer MOS transistor.Reference character 712 a denotes a polysilicon lead-out electrodebrought into direct contact with the N-type high concentration region.The top surface of the polysilicon lead-out electrode 712 b is formed ofa metal silicide. Reference numeral 713 also denotes a silicon oxidefilm insulating the gate electrode from a metal first layer, 721denoting the metal first layer shading the floating diffusion section.Reference numeral 722 denotes an interlayer insulating film insulatingthe metal first layer from a metal second layer, 723 denoting the metalsecond layer, 724 denoting an interlayer insulating film insulating themetal second layer from a metal third layer, 725 denoting the metalthird layer, and 726 denoting a passivation film.

In the present embodiment as in the second embodiment, the aliasingincident from the top surface on the floating diffusion is reduced byforming the uppermost layer of the polysilicon gate into a metalsilicide film, and at the same time, electrons of electron-hole pairs731 b generated at the end of the photodiode by obliquely incident light731 a, are collected to the cathode 703 of the photodiode by P-typeisolation layer 704 b, P-type well layer 705 b and the field stop layer714, without diffusing into the floating diffusion side.

In this way, according to the present embodiment, it is possible tosuppress the diffusion from the inside of the silicon into the floatingdiffusion. The combination of the silicide and the potential barriermakes it possible to eliminate the aliasing more effectively.

This application claims priority from Japanese Patent Application No.2004-042939 filed on Feb. 19, 2004, which is hereby incorporated byreference herein.

1-9. (canceled)
 10. A solid-state image pick-up device comprising: aphotoelectric conversion section; a signal amplifying section; afloating diffusion for inputting a signal from said photoelectricconversion section into said signal amplifying section, wherein at leasta part of a connection path from said floating diffusion to said signalamplifying section is formed through a direct contact of said floatingdiffusion with a polysilicon, and said floating diffusion is shaded by ametal layer which is closest to said floating diffusion but is notelectrically connected with said floating diffusion; a transfer MOStransistor for transferring an output from the signal amplifying sectionas an output signal of said solid-state image pick-up device; and apotential barrier disposed between said photoelectric conversion sectionand said floating diffusion, and under said transfer MOS transistor. 11.An imaging system comprising: an image forming optical system forforming an image of light from a subject; a solid-state image pick-updevice according to claim 10, for performing photoelectric conversion ofthe formed image; and a signal processing circuit for performing digitalconversion and processing of an output signal from said solid-stateimage pick-up device.